Electrical device with test interface

ABSTRACT

An example system comprises: a master bus electrically coupled to a master multiplexer controlled by a test mode signal selecting between a master physical interface (PHY) and a slave bus of a plurality of slave buses, wherein each slave bus is electrically coupled to a respective slave multiplexer selecting between a respective slave PHY and the master bus; a plurality of electrical circuits, wherein each electrical circuit of the plurality of electrical circuits is electrically coupled to one of: the master bus or a slave bus of the plurality of slave buses; and a memory test interface electrically coupled to the master bus.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/514,685 filed on Jul. 17, 2019, which is incorporated by referenceherein.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to memory sub-systems,and more specifically, relate to managing a memory sub-system includingmemory components with different characteristics.

BACKGROUND

A memory sub-system can be a storage system, such as a solid-state drive(SSD), or a hard disk drive (HDD). A memory sub-system can be a memorymodule, such as a dual in-line memory module (DIMM), a small outlineDIMM (SO-DIMM), or a non-volatile dual in-line memory module (NVDIMM). Amemory sub-system can include one or more memory components that storedata. The memory components can be, for example, non-volatile memorycomponents and volatile memory components. In general, a host system canutilize a memory sub-system to store data at the memory components andto retrieve data from the memory components.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure.

FIG. 1 illustrates an example computing environment that includes amemory sub-system in accordance with some embodiments of the presentdisclosure.

FIG. 2 illustrates an example storage device (e.g., a managed NANDdevice) with a test interface implemented in accordance with one or moreaspects of the present disclosure.

FIG. 3 is a flow diagram of an example method of accessing memorycomponents of a memory sub-system (e.g., a storage device) in the testmode, in accordance with some embodiments of the present disclosure.

FIG. 4 is a block diagram of an example computer system in whichembodiments of the present disclosure may operate.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed to a storage device witha test interface. A memory sub-system may include a storage device thatis coupled to a central processing unit (CPU) via a peripheralinterconnect (e.g., an input/output bus, a storage area network).Examples of storage devices include a solid-state drive (SSD), a flashdrive, a universal serial bus (USB) flash drive, and a hard disk drive(HDD). Another example of a memory sub-system is a memory module that iscoupled to the CPU via a memory bus. Examples of memory modules includea dual in-line memory module (DIMM), a small outline DIMM (SO-DIMM), anon-volatile dual in-line memory module (NVDIMM), etc. In someembodiments, the memory sub-system can be a hybrid memory/storagesub-system. In general, a host system can utilize a memory sub-systemthat includes one or more memory components. The host system can providedata to be stored at the memory sub-system and can request data to beretrieved from the memory sub-system.

Implementations of the present disclosure are related to storagedevices, such as negative-AND (NAND) flash storage devices, with testinterfaces. NAND flash storage devices support different type of media,including single-level cell (SLC), multilevel cell (MLC), triple-levelcell (TLC) and quad-level cell (QLC), and are available in variousdensities. Low-density NAND flash may be employed for applications suchas set-top boxes (STBs), digital televisions (DTVs), and digital signalcontrollers (DSCs), while high-density NAND flash is commonly used indata-heavy applications like solid state drives (SSDs), tablets, and USBdrives. A NAND flash storage device may be managed by a controller,either internal or external, which may perform error code correction(ECC), bad block management, and wear leveling. There are two primarytypes of NAND: raw and managed. Raw NAND requires an externalcontroller, but demonstrates the lowest cost per a unit of memory.Conversely, managed NAND includes an embedded controller to handle wearleveling, bad block management and ECC, and thus provide simpler designsolutions and a better time-to-market. Managed NAND devices are commonlyused in smartphones, tablets, and other similar portable computingdevices.

Examples of managed NAND devices include eMultiMediaCard (eMMC) devices,on-die ECC NAND devices, SSDs, embedded USB devices, Universal FlashStorage (UFS) devices, Secure Digital Card (SD) and Micro SD/USBdevices, as well as multichip packages (MCPs). In particular, eMMCdevices are high-capacity NAND flash devices combined with a high-speedMMC controller in a single package. Such devices are commonly used in awide range of networking, industrial, and automotive applications.On-die ECC NAND devices are hybrid devices of raw and fully managedNAND; ECC is integrated while wear leveling and bad block management arehandled by the host controller. SSDs are NAND-based drives that enhancereliability, reduce power, and provide faster performance compared tohard disk drives (HDDs). Embedded USB devices bring the density andreliability of an SSD to networking and embedded applications with asimple USB connector. Universal Flash Storage (UFS) devices have ahigh-performance storage interface for applications that require fastersequential and random performance over eMMC with low power consumption.Secure Digital Card (SD) and Micro SD/USB devices are commonly used forapplications that require flash memory to be easily removed orinstalled. NAND flash memory is also commonly used in MCPs where it ispaired with Mobile LPDRAM in a variety of form factors.

Endurance of the storage media is an important characteristic of flashmemory devices. When data is written to and/or erased from a memory cellof a memory component, the memory cell may be damaged. As the number ofwrite operations and/or erase operations performed on a memory cellincreases, the probability that the data stored at the memory cellincluding an error increases as the memory cell is increasingly damaged.A characteristic associated with the endurance of the memory componentis the number of write operations or a number of program/eraseoperations performed on a memory cell of the memory component. If athreshold number of write operations performed on the memory cell isexceeded, then data can no longer be reliably stored at the memory cellas the data can include a large number of errors that cannot becorrected.

Accordingly, an important feature of a managed NAND device is theability to electrically isolate the NAND memory components from thecontroller in order to directly query the NAND memory components, e.g.,to facilitate identification of a single faulty NAND memory component.In an illustrative example, testing a storage device may involveiterating through all memory components in order to directly query eachmemory component. Querying an individual memory component may involveperforming one or more cycles of writing a test data pattern, readingthe data back and comparing the data read from the memory component tothe test data pattern that was written to the memory component. Adifference between the data read from the memory component and the testdata pattern may indicate that the memory component is faulty.

In common implementations, the managed NAND device may be provided by asystem-on-chip or an integrated circuit, all the components of which arelocated on a single substrate having a standard form factor.Accordingly, additional test pins for accessing the internal bus of themanaged NAND device in the test mode are placed on the substrate and maybe connected to a test equipment (e.g., a personal computer equippedwith an adapter supporting the requisite bus protocol). However, latestmanaged NAND specifications (such as UFS 3.0/4.0) require support ofmultiple internal buses (e.g., up to four buses) for connecting to NANDmemory components. Accordingly, placing the requisite number of testpins and routing their connections to multiple internal buses maypresent a design challenge in view of the limited physical dimensions ofthe substrate.

Aspects of the present disclosure address the above and otherdeficiencies by providing a memory sub-system including a storage device(such as a managed NAND device) with a test interface, in which oneinternal bus of the managed NAND device is designated as the master bus,while other internal buses are designated as slave buses. The buses areinterconnected via bus multiplexers, thus allowing a single set of testpins connected to the maser bus to be utilized for accessing all memorycomponents.

Thus, only the master bus is equipped with a set of test pins whichsupport the requisite signals, including Address Latch Enable (ALE),Chip Enable (CE #), Command Latch Enable (CLE), Data Strobe (DQS), Data(DQx), Read Enable (RE #), Write Enable (WE), and/or Ready/Busy (R/B #),etc. A bus multiplexer is connected to each of the buses, such that themaster bus multiplexer selects between the physical interface (PHY) ofthe master bus and one of the slave buses, while each slave busmultiplexer selects between a respective PHY of the slave bus or themaster bus. The multiplexers are controlled by a test mode signal, whichthus controls which of the buses is connected to the test pins. Inaddition, the bus directions (read/write) are controlled by a directionsignal, as described in more detail herein below with references toFIGS. 1-2 .

Utilizing bus multiplexing for providing a test interface may resolvethe above-referenced design challenges related to the need to place therequisite number of test pins on the limited surface of the substrate.Furthermore, utilizing the bus multiplexing may result in a reduceddevice cost and power consumption due to limiting the energy dissipationby reducing the routing paths.

FIG. 1 illustrates an example computing system 100 that includes amemory sub-system 110 in accordance with some embodiments of the presentdisclosure. The memory sub-system 110 can include storage media, such asmemory components 112A to 112N. The memory components 112A to 112N canbe volatile memory components, non-volatile memory components, or acombination of such. In some embodiments, the memory sub-system is astorage device, such as a managed NAND device. In some embodiments, thememory sub-system 110 is a hybrid memory/storage sub-system. In general,the computing system 100 can include a host system 120 that uses thememory sub-system 110. For example, the host system 120 can write datato the memory sub-system 110 and read data from the memory sub-system110.

The host system 120 can be a computing device such as a desktopcomputer, laptop computer, network server, mobile device, or suchcomputing device that includes a memory and a processing device. Thehost system 120 can include or be coupled to the memory sub-system 110so that the host system 120 can read data from or write data to thememory sub-system 110. The host system 120 can be coupled to the memorysub-system 110 via a physical host interface. As used herein, “coupledto” generally refers to a connection between components, which can be anindirect communicative connection or direct communicative connection(e.g., without intervening components), whether wired or wireless,including connections such as electrical, optical, magnetic, etc.Examples of a physical host interface include, but are not limited to, aserial advanced technology attachment (SATA) interface, a peripheralcomponent interconnect express (PCIe) interface, universal serial bus(USB) interface, Fibre Channel, Serial Attached SCSI (SAS), etc. Thephysical host interface can be used to transmit data between the hostsystem 120 and the memory sub-system 110. The host system 120 canfurther utilize an NVM Express (NVMe) interface to access the memorycomponents 112A to 112N when the memory sub-system 110 is coupled withthe host system 120 by the PCIe interface. The physical host interfacecan provide an interface for passing control, address, data, and othersignals between the memory sub-system 110 and the host system 120.

The memory components 112A to 112N can include any combination of thedifferent types of non-volatile memory components and/or volatile memorycomponents. An example of non-volatile memory components includes anegative-and (NAND) type flash memory. Each of the memory components112A to 112N can include one or more arrays of memory cells such assingle level cells (SLCs) or multi-level cells (MLCs) (e.g., triplelevel cells (TLCs) or quad-level cells (QLCs)). In some embodiments, aparticular memory component can include both an SLC portion and a MLCportion of memory cells. Each of the memory cells can store one or morebits of data (e.g., data blocks) used by the host system 120. Althoughnon-volatile memory components such as NAND type flash memory aredescribed, the memory components 112A to 112N can be based on any othertype of memory such as a volatile memory. In some embodiments, thememory components 112A to 112N can be, but are not limited to, randomaccess memory (RAM), read-only memory (ROM), dynamic random accessmemory (DRAM), synchronous dynamic random access memory (SDRAM), phasechange memory (PCM), magneto random access memory (MRAM), negative-or(NOR) flash memory, electrically erasable programmable read-only memory(EEPROM), and a cross-point array of non-volatile memory cells. Across-point array of non-volatile memory can perform bit storage basedon a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. Additionally, in contrast to manyflash-based memories, cross-point non-volatile memory can perform awrite in-place operation, where a non-volatile memory cell can beprogrammed without the non-volatile memory cell being previously erased.Furthermore, the memory cells of the memory components 112A to 112N canbe grouped as memory pages or data blocks that can refer to a unit ofthe memory component used to store data.

The memory system controller 115 (hereinafter referred to as“controller”) can communicate with the memory components 112A to 112N toperform operations such as reading data, writing data, or erasing dataat the memory components 112A to 112N and other such operations. Thecontroller 115 can include hardware such as one or more integratedcircuits and/or discrete components, a buffer memory, or a combinationthereof. The controller 115 can be a microcontroller, special purposelogic circuitry (e.g., a field programmable gate array (FPGA), anapplication specific integrated circuit (ASIC), etc.), or other suitableprocessor. The controller 115 can include a processor (processingdevice) 117 configured to execute instructions stored in local memory119. In the illustrated example, the local memory 119 of the controller115 includes an embedded memory configured to store instructions forperforming various processes, operations, logic flows, and routines thatcontrol operation of the memory sub-system 110, including handlingcommunications between the memory sub-system 110 and the host system120. In some embodiments, the local memory 119 can include memoryregisters storing memory pointers, fetched data, etc. The local memory119 can also include read-only memory (ROM) for storing micro-code.While the example memory sub-system 110 in FIG. 1 has been illustratedas including the controller 115, in another embodiment of the presentdisclosure, a memory sub-system 110 may not include a controller 115,and may instead rely upon external control (e.g., provided by anexternal host, or by a processor or controller separate from the memorysub-system).

In general, the controller 115 can receive commands or operations fromthe host system 120 and can convert the commands or operations intoinstructions or appropriate commands to achieve the desired access tothe memory components 112A to 112N. The controller 115 can beresponsible for other operations such as wear leveling operations,garbage collection operations, error detection and error-correcting code(ECC) operations, encryption operations, caching operations, and addresstranslations between a logical block address and a physical blockaddress that are associated with the memory components 112A to 112N. Thecontroller 115 can further include host interface circuitry tocommunicate with the host system 120 via the physical host interface.The host interface circuitry can convert the commands received from thehost system into command instructions to access the memory components112A to 112N as well as convert responses associated with the memorycomponents 112A to 112N into information for the host system 120.

The memory sub-system 110 can also include additional circuitry orcomponents that are not illustrated. In some embodiments, the memorysub-system 110 can include a cache or buffer (e.g., DRAM) and addresscircuitry (e.g., a row decoder and a column decoder) that can receive anaddress from the controller 115 and decode the address to access thememory components 112A to 112N.

In certain implementations, the memory sub-system may be represented bya managed NAND storage device that may be implemented as a singleintegrated circuit (or a system-on-chip), in which all components,including the memory components 112A-112N and the controller 115 arelocated on a single substrate having a standard form factor, asdescribed in more detail herein below with reference to FIG. 2 . Invarious illustrative examples, the storage device may support a standardphysical interface and pin assignments, e.g., 48-pin TSOP or 48-pin WSOPpackaging for 8-bit or 16-bit data access.

FIG. 2 illustrates an example storage device 200 (e.g., a managed NANDdevice) with a test interface implemented in accordance with one or moreaspects of the present disclosure. In the illustrative example of FIG. 2, the storage device 200 is implemented as a single integrated circuit(or a system-on-chip), all components of which are locate on a singlesubstrate 210. The storage device 200 includes multiple memorycomponents 212A-212N, each of which may include one or more arrays ofmemory cells, such as single level cells (SLCs) or multi-level cells(MLCs) (e.g., triple level cells (TLCs) or quad-level cells (QLCs)). Insome embodiments, a particular memory component can include both an SLCportion and a MLC portion of memory cells. Each of the memory components212A-212N is electrically coupled to one of the buses 214A-214K. The bus214A is designated as the master bus, while the buses 214B-214K aredesignated as slave buses. While four buses are shown in theillustrative example of FIG. 2 , of which three buses are designated asslave buses, other implementations of this disclosure may includevarious other numbers of slave buses which are interconnected to themaster bus in the manner shown in FIG. 2 .

The storage device 200 may further include an application-specificintegrated circuit (ASIC) 215, which may implement various memorycontroller functions, such as ECC, bad block management, wear leveling,and/or other functions directed to supporting a requisite memory accessprotocol at the physical interfaces (PHYs) 216A-216K. It should be notedthat the circuitry employed for performing the memory controllerfunctions is omitted from FIG. 2 for clarity and conciseness.

Each PHY 216A-216K is electrically coupled to a corresponding bus214A-214K, such that the master bus 214A is electrically coupled to themaster PHY 216A, while each of the slave buses is electrically coupledto a respective slave PHY 216B-216K. It should be noted that “master”and “slave” designations of the PHYs 216 are utilized herein solely forthe purposes of simplifying the description when referring to therelationships between a bus and a corresponding PHY, while all the PHYs,irrespective of their “master” and “slave” designation, may bephysically implemented in a similar manner.

In order to prevent undesirable signal reflection in the buses, each ofthe buses may be electrically coupled to the ground via a terminatingresistor matching the characteristic impedance of the bus. Inparticular, the master bus 212A may be electrically coupled to theground via the master bus terminating resistor 217A, while each slavebus 212B-212K may be electrically coupled to the ground via a respectiveslave bus terminating resistor 217B-217K.

The master bus 214A may be electrically coupled to the test interface218, which may include a plurality of pins located on the substrate forconnecting to the testing equipment 220 (e.g., a personal computerequipped with an adapter supporting the requisite bus protocol). Itshould be noted that the test equipment 220 does not constitute anintegral part of the storage device 200 and as such is shown in FIG. 1for reference purposes only, in order to illustrate the functionaldesignation of the test interface 218. The test pins of the testinterface 218 may support various requisite signals, including AddressLatch Enable (ALE), Chip Enable (CE #), Command Latch Enable (CLE), DataStrobe (DQS), Data (DQx), Read Enable (RE #), Write Enable (WE), and/orReady/Busy (R/B #).

The ALE and CLE signals may be utilized by the host to indicate the typeof the bus cycle (command, address, or data). The CE # signal may beutilized by the host to select the target: when CE # is high and thetarget is in the ready state, the target goes into a low-power standbystate; when CE # is low, the target is selected. The WE signal may beutilized by the host to control the latching of commands, addresses, andinput data: data, commands, and addresses are latched on the rising edgeof WE. The DQS signal may indicate the data valid window. The DQx signalis captured on the edges of DQS, and may be used in some datainterfaces. The RE # signal enables serial data output. The R/B # signalindicates the target status: when low, the signal indicates that one ormore logical unit number (LUN) operations are in progress.

As noted herein above, the storage device 200 should be able toelectrically isolate the memory components 212A-212N from the PHYs216A-216K in order to directly query the memory components, e.g., tofacilitate identification of a single faulty memory component 212. In anillustrative example, testing the storage device 200 may involveiterating through all memory components 212A-212N in order to directlyquery each memory component. Querying an individual memory component212A-212N may involve performing one or more cycles of writing a testdata pattern, reading the data back and comparing the data read from thememory component to the test data pattern that was written to the memorycomponent. A difference between the data read from the memory componentand the test data pattern may indicate that the memory component isfaulty.

Accordingly, in order to enable access to a selected memory component212A-212N through the test interface 218 while isolating the PHYs216A-216K, each bus 214A-214K is electrically coupled to a respectivemultiplexer 222A-222K, which is controlled by a test mode signal 224 toenable an electric path between the selected memory component 212A-212Nand the test interface 218. In particular, the master bus 214A iselectrically coupled to the K:1 multiplexer 222A, where K is the totalnumber of buses in the storage device 200. Accordingly, the master busmultiplexer 222A, controlled by the test mode signal 224, is employed toselect whether the master PHY 216A or one of the slave buses 214B-214Kis coupled to the master bus 214A.

Similarly, each slave bus 214B-214K is electrically coupled to arespective 2:1 multiplexer 222B-222K. Each slave bus multiplexer, e.g.,multiplexer 222B, controlled by the test mode signal 224, is employed toselect whether the master bus 214A or the respective slave PHY 216B iscoupled to the slave bus 214B.

Furthermore, the buses 214A-214K are controlled using the directionsignal 226 and respective direction control elements (e.g., diodes orthyristors) 228A-228K in order to select the direction of the datatransfer (to or from the selected memory component 212). The directionsignal supplied to the master bus 214A is inverted with respect to thedirection signals supplied to each of the slave buses 214B-214K, thusensuring that the master bus 214A and the selected slave bus 214B-214Koperate in the opposite directions, i.e., for reading data from a memorycomponent 212 connected to a slave bus 214B-214K, the bus direction ofthe slave bus 214B-214K is set in such a way that the data being readfrom the selected memory component is fed through the slave bus to themaster multiplexer 222A, and then through the master bus 212A to thetest interface 218. Conversely, for writing data to a memory component212 connected to a slave bus 214B-214K, the bus direction of the masterbus 214A is set in such a way that the data being read from the testinterface 218 is fed through the master bus 214A to the selected slavebus 214B-214K via the respective slave bus multiplexer 222B-222K. Thebus cycles are asserted accordingly using the appropriate chip enable(CE #) signal to read/write data from/to the selected memory component212.

For example, for reading data from the memory component 212C connectedto the slave bus 214B, the bus direction of the slave bus 214B is set insuch a way that the data being read from the memory component 212C isfed through the slave bus 214B to the master multiplexer 222A, and thenthrough the master bus 212A to the test interface 218. In anotherexample, for writing data to the memory component 212E connected to theslave bus 214C, the bus direction of the master bus 214A is set in sucha way that the data being read from the test interface 218 is fedthrough the master bus 214A to the selected slave bus 214 c via theslave bus multiplexer 222C.

FIG. 3 is a flow diagram of an example method 300 of accessing memorycomponents of a storage device in the test mode, in accordance with someembodiments of the present disclosure. The method 300 can be performedby processing logic that can include hardware (e.g., processing device,circuitry, dedicated logic, programmable logic, microcode, hardware of adevice, integrated circuit, etc.), software (e.g., instructions run orexecuted on a processing device), or a combination thereof. In someembodiments, the method 300 is performed by the testing equipment 220 ofFIG. 2 . Although shown in a particular sequence or order, unlessotherwise specified, the order of the processes can be modified. Thus,the illustrated embodiments should be understood only as examples, andthe illustrated processes can be performed in a different order, andsome processes can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At operation 310, a computer system implementing the method mayidentify, among a plurality of memory components of a storage device tobe tested, a memory component to be accessed via the test interface. Asnoted herein above, the storage device supports directly querying of itsmemory components, e.g., in order to facilitate identification of asingle faulty memory component. Accordingly, in an illustrative example,testing the storage device may involve iterating through all memorycomponents in order to directly query each of them, e.g., by performingone or more cycles of writing a test data pattern, reading the data backand comparing the data read from the memory component to the test datapattern that was written to the memory component. A difference betweenthe data read from the memory component and the test data pattern mayindicate that the memory component is faulty.

At operation 320, the computer system may identify, among a plurality ofslave buses of the memory system, a slave bus to which the memorycomponent of interest is electrically coupled. In an illustrativeexample, the bus number may be equal to the integer quotient of thememory component number and the number of memory components per bus.

At operation 330, the computer system may assert a test mode signal toforce electrical coupling of the slave bus to the master bus. As notedherein above, the master bus is electrically coupled to a K:1multiplexer, where K is the total number of buses in the storage device,such that the master bus multiplexer, controlled by the test modesignal, is employed to select whether the master PHY or one of the slavebuses is coupled to the master bus. Similarly, each slave bus iselectrically coupled to a respective 2:1 multiplexer, which iscontrolled by the test mode signal to select whether the master bus orthe respective slave PHY is coupled to the slave bus.

At operation 340, the computer system may assert a bus direction signalto indicate a desired direction of data transfer (read or write datafrom/to the memory component of interest). As noted herein above, thedirection signal supplied to the master bus is inverted with respect tothe direction signals supplied to each of the slave buses, thus ensuringthat the master bus and the selected slave bus operate in the oppositedirections: for reading data from the memory component of interest, thebus direction of the slave bus to which the memory component isconnected is set in such a way that the data being read from the memorycomponent is fed through the slave bus to the master multiplexer, andthen through the master bus to the test interface. Conversely, forwriting data to the memory component of interest, the bus direction ofthe master bus is set in such a way that the data being read from thetest interface is fed through the master bus, via the respective slavebus multiplexer, to the slave bus to which the memory component ofinterest is connected.

At operation 350, the computer system may assert, on the master bus, achip enable (CE) signal to select the memory component of interest.

At operation 360, the computer system may assert, on the master bus,various signals to control the bus cycles. In an illustrative example,the computer system may asset a read enable (RE) signal or a writeenable (WE) signal to select the desired data transfer operation.

At operation 370, the computer system may access the memory componentvia the test interface in order to perform the desired data transferoperation. Responsive to completing operation 360, the method mayterminate.

FIG. 4 illustrates an example machine of a computer system 400 withinwhich a set of instructions, for causing the machine to perform any oneor more of the methodologies discussed herein, can be executed. In someembodiments, the computer system 400 can correspond to a host system(e.g., the host system 120 of FIG. 1 ) that includes, is coupled to, orutilizes a memory sub-system (e.g., the memory sub-system 110 of FIG. 1) or can be used to perform the operations of a test equipment (e.g., toexecute an operating system to perform operations of the test equipment220 of FIG. 1 ). In alternative embodiments, the machine can beconnected (e.g., networked) to other machines in a LAN, an intranet, anextranet, and/or the Internet. The machine can operate in the capacityof a server or a client machine in client-server network environment, asa peer machine in a peer-to-peer (or distributed) network environment,or as a server or a client machine in a cloud computing infrastructureor environment.

The machine can be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, a switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated, the term “machine” shall also betaken to include any collection of machines that individually or jointlyexecute a set (or multiple sets) of instructions to perform any one ormore of the methodologies discussed herein.

The example computer system 400 includes a processing device 402, a mainmemory 404 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM(RDRAM), etc.), a static memory 404 (e.g., flash memory, static randomaccess memory (SRAM), etc.), and a data storage system 418, whichcommunicate with each other via a bus 430.

Processing device 402 represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device can be a complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice 402 can also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. The processing device 402 is configuredto execute instructions 424 for performing the operations and stepsdiscussed herein. The computer system 400 can further include a networkinterface device 408 to communicate over the network 420.

The data storage system 418 can include a machine-readable storagemedium 424 (also known as a computer-readable medium) on which is storedone or more sets of instructions 424 or software embodying any one ormore of the methodologies or functions described herein. Theinstructions 424 can also reside, completely or at least partially,within the main memory 404 and/or within the processing device 402during execution thereof by the computer system 400, the main memory 404and the processing device 402 also constituting machine-readable storagemedia. The machine-readable storage medium 424, data storage system 418,and/or main memory 404 can correspond to the memory sub-system 110 ofFIG. 1 .

In one embodiment, the instructions 424 include instructions toimplement functionality corresponding to a characteristic component(e.g., the characteristic component 113 of FIG. 1 ). While themachine-readable storage medium 424 is shown in an example embodiment tobe a single medium, the term “machine-readable storage medium” should betaken to include a single medium or multiple media that store the one ormore sets of instructions. The term “machine-readable storage medium”shall also be taken to include any medium that is capable of storing orencoding a set of instructions for execution by the machine and thatcause the machine to perform any one or more of the methodologies of thepresent disclosure. The term “machine-readable storage medium” shallaccordingly be taken to include, but not be limited to, solid-statememories, optical media, and magnetic media.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure can refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for theintended purposes, or it can include a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program can be stored in a computerreadable storage medium, such as, but not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems can be used with programs in accordance with the teachingsherein, or it can prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of thedisclosure as described herein.

The present disclosure can be provided as a computer program product, orsoftware, that can include a machine-readable medium having storedthereon instructions, which can be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). In someembodiments, a machine-readable (e.g., computer-readable) mediumincludes a machine (e.g., a computer) readable storage medium such as aread only memory (“ROM”), random access memory (“RAM”), magnetic diskstorage media, optical storage media, flash memory components, etc.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to specific example embodiments thereof. Itwill be evident that various modifications can be made thereto withoutdeparting from the broader spirit and scope of embodiments of thedisclosure as set forth in the following claims. The specification anddrawings are, accordingly, to be regarded in an illustrative senserather than a restrictive sense.

What is claimed is:
 1. A system, comprising: a master bus electricallycoupled to a master multiplexer controlled by a test mode signal toselect between a master physical interface (PHY) and a slave bus of aplurality of slave buses, wherein each slave bus is electrically coupledto a respective slave multiplexer to select between a respective slavePHY and the master bus; a plurality of electrical circuits, wherein eachelectrical circuit of the plurality of electrical circuits iselectrically coupled to one of: the master bus or a slave bus of theplurality of slave buses; and a test interface electrically coupled tothe master bus.
 2. The system of claim 1, wherein the master bus furthercomprises a master direction control element controlled by a directionsignal.
 3. The system of claim 1, wherein each slave bus of theplurality of slave buses further comprises a respective slave directioncontrol element controlled by a reversed direction signal.
 4. The systemof claim 1, wherein the master bus is electrically coupled to a groundvia a master bus terminating resistor.
 5. The system of claim 1, whereineach slave bus of the plurality of slave buses is electrically coupledto a ground via a respective slave bus terminating resistor.
 6. Thesystem of claim 1, wherein the test interface comprises a chip enablesignal to select an electrical circuit of the plurality of electricalcircuits.
 7. The system of claim 1, wherein the test interface comprisesat least one of: a read enable (RE) signal or a write enable (WE)signal.
 8. The system of claim 1, further comprising: anapplication-specific integrated circuit (ASIC) electrically coupled tothe master bus and the plurality of slave buses.
 9. An integratedcircuit, comprising: a substrate; a plurality of electrical circuitsdisposed on the substrate, wherein each electrical circuit of theplurality of electrical circuits is electrically coupled to one of: amaster bus or a slave bus of a plurality of slave buses; and a testinterface electrically coupled to the master bus, wherein the testinterface comprises a test mode signal to manage selective electricalcoupling of the master bus to one of: a master physical interface (PHY)or a slave bus of the plurality of slave buses, wherein each slave busof the plurality of slave buses is selectively electrically coupled toone of: a respective slave PHY or the master bus.
 10. The integratedcircuit of claim 9, wherein the master bus is electrically coupled to amaster multiplexer controlled by the test mode signal selecting betweenthe master PHY and a slave bus of the plurality of slave buses.
 11. Theintegrated circuit of claim 9, wherein each slave bus is electricallycoupled to a respective slave multiplexer selecting between a respectiveslave PHY and the master bus.
 12. The integrated circuit of claim 9,wherein the master bus further comprises a master direction controlelement controlled by a direction signal.
 13. The integrated circuit ofclaim 9, wherein each slave bus of the plurality of slave buses furthercomprises a respective slave direction control element controlled by areversed direction signal.
 14. The integrated circuit of claim 9,wherein the test interface comprises a chip enable signal to select anelectrical circuit of the plurality of electrical circuits.
 15. Theintegrated circuit of claim 9, wherein the test interface comprises atleast one of: a read enable (RE) signal or a write enable (WE) signal.16. A method, comprising: identifying, among a plurality of electricalcircuits, an electrical circuit to be accessed via a test interfaceelectrically coupled to a master bus; identifying, among a plurality ofslave buses of a storage device, a slave bus electrically coupled to theelectrical circuit; asserting a test mode signal to manage electricalcoupling of the slave bus to the master bus; and accessing theelectrical circuit via the test interface.
 17. The method of claim 16,wherein accessing the electrical circuit further comprises: asserting,on the master bus, a chip enable (CE) signal to select the electricalcircuit.
 18. The method of claim 16, wherein accessing the electricalcircuit further comprises: asserting, on the master bus, at least oneof: a read enable (RE) signal or a write enable (WE) signal.
 19. Themethod of claim 16, wherein accessing the electrical circuit furthercomprises: asserting a bus direction signal to indicate a direction ofdata transfer.
 20. The method of claim 16, wherein the electricalcoupling of the slave bus to the master bus is performed by a slave busmultiplexer controlled by the test mode signal.